The invention relates to a sputtering cathode for coating substrates in cathode sputtering apparatus having a cathode base body and a hollow target disposed thereon. The target has at least one planar sputtering surface of annular shape, for example, which is surrounded by at least two continuous concentric projections. A magnet system with pole faces of opposite polarity lies on both sides of the target for the production of magnetic lines of force running substantially parallel to the sputtering surface.
Sputtering cathodes for coating substrates in cathode sputtering apparatus are known (U.S. Pat. No. 4,933,064, U.S. Pat. No. 4,486,287), which consist essentially of a cathode base body, a hollow target disposed thereon, as well as a magnet system encompassing the target, and which are called ZPT hollow magnetrons (ZPT=target between poles) on account of the way they are constructed. The hollow targets commonly used in such hollow magnetrons have continuous concentric projections, while the wall surfaces of the projections of the target adjoining the sputtering surfaces have thus far been arranged perpendicular to the sputtering surface in the sputtering direction.
This type of construction produces two contrary phenomena which heretofore have not been reconcilable with one another. On the one hand it would be desirable to achieve magnetic lines of force running parallel to the sputtering surface in order to achieve the highest possible sputtering rates. On the other hand, the magnetic lines of force issue in a substantially perpendicular direction from the one wall surface of the one projection of the target, namely the wall surface adjoining the sputtering surface, and after crossing the sputtering surface they return in a substantially vertical direction into the other, opposite wall surface of the other projection. Since these wall surfaces are penetrated by the magnetic lines of force in a substantially perpendicular direction, they are no longer available for the sputtering; on the contrary, the material removed from the sputtering surface during the sputtering process is deposited on these wall surfaces and disadvantageously forms a coating which is not desired on these surfaces. After a sufficient coating thickness has been established by the sputtering process using a metal target material, the coating that forms spalls off in the described target areas, rendering the target useless and definitely leading to the failure of the entire sputtering apparatus.
In the reactive operation of the sputtering cathode an undesired coating of the target margins with dielectric material takes place, which leads to arcing and thus also to the shut-down of the sputtering process.
It is therefore the object of the invention to prevent the coating of the wall surfaces of the target projections with target material and to preserve the advantages of the hollow magnetron, i.e., to achieve a good lateral electrostatic confinement of the plasma and good utilization of the target material.